Commercially available interactive projection systems, such as “Smart Boards”, often use hand-held input devices to interact with the projected image. Such hand-held input devices can include active infrared, ultrasonic and/or RF transmitters and/or receivers. These input devices are used for location of the device relative to the projected image, and can also function to activate a signal to effect a change in the projected image. Such input devices can be formed, for example, in the shape of a marker or a pen.
Active input devices generally can include light generation devices, while passive devices reflect or absorb light that is produced elsewhere. Active input devices require a power source, such as an internal battery or power delivered via a connecting wire. Wired devices can be cumbersome to use, and battery powered devices require the battery to be replaced and/or recharged, making active input devices less than ideal. However, available active devices can provide clear, strong input information, whereas simple passive devices can suffer from interference with ambient signals, masking the intended input signal.